This invention relates to a control method and apparatus for suppressing the swing of a load suspended on a rope, for example a load suspended from a trolley of an overhead traveling crane, a container suspended from a trolley of a container crane or a container carrier, or a grab bucket on a grab bucket crane or an unloader for loading and unloading bulk material, during travel of the grab bucket, or the like.
As is commonly known, methods for suppressing the swing of a suspended load during acceleration, deceleration or steady travel can be generally divided into mechanical steadying methods and electronic steadying methods.
Mechanical steadying methods include methods for stopping swinging by providing, for example, a guide mast on the trolley itself, or by focusing on the structure of a container crane or the container itself, or by using special rope arrangements and rope tension devices or hydraulic cylinders capable of suppressing the swing.
Electronic steadying methods include methods wherein the steadying control is carried out by detecting the swing angle or the swing speed of the suspended load and feeding this back to the drive system, or by computing and ordering a speed pattern with which swing can be eliminated at the end of acceleration (for example the crane rope steadying control method of Japanese Patent Publication No. Sho 45-4020).
This electronic steadying control includes a closed loop type control wherein steadying is carried out by detecting the swing angle of the suspended load and feeding this back to the drive system through a suitable compensating element, and an open loop type control wherein, on the basis of solutions of equations of motion pertaining to the suspended load, swing angles and swing speeds during acceleration and deceleration are predicted, and acceleration and deceleration rates and times by which steadying can be achieved are ordered (for example the suspended type crane rope steadying control apparatus of Unexamined Japanese Utility Model Publication No. Sho 57-158670).
With a conventional method, as disclosed in Japanese Patent Publication No. Sho 45-4020, swing angle detecting means are fundamentally necessary. In this method, the swing angle of the rope is mechanically detected but, because the rope moves during hoisting and lowering, the structure of the linkage device must fulfill the conflicting requirements of certain linkages to the rope and slidability with respect thereto, and the resulting design has inevitably been complicated and lacking in reliability.
To solve this problem, an optical swing angle detecting system using a light source, a camera and an image processing device has recently been proposed.
Although this system has no mechanical linkage with the moving rope, deterioration due to dust is a concern because of its optical nature. Furthermore, the accurate alignment of the light source and camera, and processing to compute the swing angle from an image, incur excessive costs. Also, for reasons relating to crane structure, the camera is generally mounted in the vicinity of the hoisting winch of the trolley, and requires installation space there. Also, supposing now that the trolley acceleration is 0.5 m/sec.sup.2, even considering the maximum swing angle, its value is quite small, at 0.102 rad, and accurate alignment of the camera and the light source is necessary from the point of view of swing angle detection precision. Also necessary is accurate camera control. Thus, the detecting apparatus is unavoidably complicated and delicate.
To solve these kinds of problems, swing angle models and swing angle observers for estimating swing angles by calculation from motor speed, trolley speed and rope length or the like, without using a swing angle detecting apparatus, have also been studied. Unfortunately, because they are quite complex, make large errors, and cannot handle cases where there is an initial swing or outside disturbance, they have not achieved practical applicability.